Stonemont Solutions Blog: Best Practices for Evaluating Changes in Concrete Performance

When things are going well, concrete is breaking beyond design strength, concrete finish times are ideal, hardened concrete exhibits little to no cracking, and discoloration is simply unheard of. It is easy to become complacent when things are going well! This sense of security has a way of getting shattered as business expands into new territory. It seems that suddenly issues start appearing out of nowhere. This is usually when concrete producers first come to terms with the value of centralizing data into a quality control system such a StonemontQC. As the saying goes, you can’t manage what you don’t measure. StonemontQC is a comprehensive quality management system that can help prevent issues before they become customer complaints. So after entering data into the system, it’s time to put that data to good use to help prevent issues or help evaluate existing issues you may be having. The following are some recommendations to use when researching and evaluating existing issues using the data that you worked so hard to collect.

Evaluate Data from a Single Source – When trouble shooting issues, it is often best to evaluate data from one source at a time.

You should consider whether or not the data you are reviewing is from a single plant and used a single cement, additive, admixture, and aggregate source. Any changes in sources can impact all of the mixes coming from a single location and should definitely be considered a change in process. There are ways in StonemontQC to track process changes and also ways to identify process changes using the analysis and charting tools.
You should review batching records using graphical tools to identify large differences in target versus actual batched amounts. StonemontQC includes a batch monitoring tool that can automatically send an email when batches are out-of-tolerance. Improving batching can be an important component to improving consistent quality concrete.

Evaluate a single mix design – If issues seem to be isolated to a single mix, look for the following;

Changes in cementitious content will effect concrete strength and set time among other things.
Changes in aggregate properties or blend can affect finishability, placeability, and strength among other things.
Changes or the addition of an admixture can create both intended and unintended changes to concrete performance. Below are just some of the more common issues that can be created.

Mid-range and high-range water reducers may impact set times and air dosage efficiencies as well as strength results.
Fibers appear to stiffen up concrete which may lead to additional water being added to the mix to compensate.
Retarders may increase how long a slab on grade is vulnerable to plastic shrinkage cracking.
Hot water may increase overall water demand affecting strength results and increasing the chance of cracking.
Accelerators may increase overall water demand and increase early strength results yet lower later strength results.
Changes in air entrainment dosages may affect air content and strength results.

Evaluate from a Single Project – When issues cannot be isolated to mix changes, filtering the data down to the project that is having the issue is a simple process in StonemontQC provided that the project was assigned to the sample at the time of entry.

Travel time can have a big impact on the plastic properties of the mix such as slump, temperature, and air entrainment.
Added water on the job site can impact the concrete plastic properties, set time and strength.
Different technicians/labs/equipment effect results

Scales affect unit weight results so make sure the calibration is up to date
Initial cure can have a dramatic effect on strength results, make sure cylinders are being cured according to the test method
Air pot calibration and condition can effect air results, comparing calculated gravimetric air results can be helpful in verifying any potential issues
Non-calibrated thermometers effect temperature readings, this can muddy research into potential temperature issues
Technician techniques can impact all results
Transportation to lab can impact results
At the lab, the handling, curing, and breaking of cylinders/cubes can all impact strength results. StonemontQC includes low strength and strength classification tools for evaluating overall and within-batch test results to help identify any potential strength testing issues.

Adjust the Time Frame of your Study – New issues often crop up during the fall and spring. Looking at data over various time frames can help identify issues that may be temperature and/or weather specific.

Ambient conditions affect concrete properties and performance. Ambient temperatures can affect the concrete temperatures, water demands, and set times. Humidity and wind plays a big part in plastic shrinkage cracking
Adjusting time frames anywhere from a single day to a year may uncover issues that could only be related to a single day or pour, to identifying seasonally related issues.

StonemontQC includes many tools that can help prevent issues from occurring including the use of our real-time batch monitoring, charting and analysis tools, and automated failure alerts and evaluation reports. However, if an issue does occur, the robust analysis and reporting tools in StonemontQC will help you identify the issue quickly. These tools include our statistical analysis, run charts and control charts and cusum charts, low strength analysis, target strength analysis, and strength classification tools.